An exhaust device which purifies and exhausts gas generated by the operation of an engine is generally provided in a vehicle.
The exhaust device may include an exhaust manifold which collects exhaust gas emitted from the respective cylinders of an engine, a catalytic converter which removes noxious components contained in exhaust gas, a muffler which reduces exhaust sound and an exhaust pipe which connects the exhaust manifold, the catalytic converter and the muffler together and through which exhaust gas passes.
Here, the muffler is a device which absorbs sound of exhaust gas emitted from an engine and is provided with a filter pipe therein.
The filter pipe is a tubular member which is connected to the exhaust pipe and passes linearly the inside of the muffler and is provided with a plurality of through holes on an outer circumference thereof so as to emit noise to the outside, and is formed such that an inner diameter of one side thereof is expanded.
In more detail, in the conventional manufacturing process of the filter pipe, a plurality of holes are formed in a mother material and then this mother material is cut in a predetermined size as a planar member. Subsequently, the cut planar member is bent to form a hollow cylindrical shape and then both end portions are adhered to one another by welding so as to form a tubular body with a uniform inner diameter. Finally, an expanded portion having different inner diameter is formed at one side of the tubular body by inserting an expanding mold having a diameter greater than the inner diameter of the tubular body into the tubular body or by inserting a jaw of a pipe-expanding device into one side of the tubular body and spreading to the outside
That is, the enlarged portion is formed by a process of expanding the mother material in a radially outside direction, and it can have a greater size as the thickness of the mother material is thicker.
However, with the trend of weight reduction of a vehicle, a thickness of a part of a vehicle is gradually decreased.
Accordingly, the size of the enlarged portion is limited to a predetermined size due to the low expanding ratio, and it is impossible to insert an exhaust pipe into the expanded portion, so an additional shrinking process of the exhaust pipe is necessary, and this may cause an increase of exhaust pressure which may deteriorate the performance of an engine.
In addition, the expanding process of the filter pipe is performed after the welding process, so the welded portion may be damaged by the force applied during the expanding process.